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Science School – Out of Africa


 

The ‘Out of Africa’ model in human evolution is an idea – and it’s an idea that is supported by all the evidence – that humans as a species originated in Africa and that they then expanded out of Africa.  So the population grew and started to spill out of Africa, and human beings then started to colonise the globe.  So they moved into Asia, they moved into Europe and eventually, when the ice sheet started to melt in North America, they managed to move down into the Americas as well.

And it’s a story that we know from looking at a few different lines of evidence.  And this is great, because it’s almost like you can use one bit of evidence to test the story against another bit of evidence.  So it’s a story, for instance, that Chris Stringer, who is the Head of Paleoanthropology – that’s the study of human origins – at the Natural History Museum, it’s a story that he suspected from looking at the skulls of ancient humans.  So he was arguing for this idea of humans coming out of Africa before in fact we had much evidence in the way of genetics.  Now we’ve got a lot of evidence from genetics.

So, genetics studies of living people today show how all of our DNA is related, and you can build up a big family tree of everybody on the planet today.  And that big family tree has a particular structure to it.  It has branches in particular places and you can kind of lay it across a map of the world and it shows you where these ancient migrations were and it shows you humans leaving Africa.  And you can even time it as well because you can look at the number of mutations that have happened in the DNA and you can time that exit out of Africa.

So we know this story about the yuma species originating in Africa and then expanding out of Africa from looking both at anatomy, the shape of skulls for instance, but also from looking at the DNA of living people today.  

And we can get ancient DNA as well.  So we can actually look into fossils of ancient humans too and extract ancient DNA as well.  And one of the exciting things that’s happened quite recently has been getting ancient DNA out of another species, and these are the Neanderthals.  Neanderthals are a species that were in Europe before our ancestors…our modern human or homo sapien ancestors came into Europe, they were there, they were the indigenous population.  And a lot of scientists thought that Neanderthals and modern humans were completely separate species and that they never interbred and that perhaps modern humans killed off the Neanderthals, or perhaps they just couldn’t cope with this competitor in the landscape eating the same food that they were eating.  But we know now from looking at the genomes, so all of the DNA of an individual, looking at several human genomes and looking at Neanderthal DNA which has been extracted from very, very ancient fossils going back about 40,000 years, that there does seem to be Neanderthal DNA in some modern human genomes.  So that suggests that there was interbreeding between our two species and in fact I’ve got a relatively high level of Neanderthal DNA in me!  Which my dad claims is from my mum’s side of the family and my mum claims it’s from my dad’s side of the family!

And if you want to find out more about that, go to the Natural History Museum and look at their exhibition!